Chopper was a member of the Grand Army of the Republic as a clone trooper during the Clone Wars. Serving as a soldier within the squad of Clone Sergeant "Slick", Chopper and his fellow troopers fought as part of the Jedi-commanded army dispatched by the Galactic Republic to defend the planet of Christophsis against the Confederacy of Independent Systems. Secretly, Chopper had begun amassing fingers from B1-series battle droids as wartime keepsakes, which he then crafted into a necklace. To the shock and revulsion of his fellow clones, Clone Commander Cody and Clone Captain Rex discovered Chopper's breach of regulations while they were investigating a clone spy within their ranks, although Chopper vehemently denied being a traitor.
Slick, who was, in reality, the spy they sought, attempted to shift the blame for his betrayal onto Chopper. When Chopper resisted, the sergeant inadvertently exposed his awareness of classified details and made an attempt to flee the Republic base. Ultimately, his own squad captured the clone double-agent and placed him under arrest, but only after he had managed to sabotaging a significant portion of the Republic's military provisions.
Like all [clone troopers](/article/clone_trooper], the trooper known as Chopper was cloned on the [planet](/article/planet] of Kamino utilizing the genetic material obtained from the bounty hunter Jango Fett, who functioned as the clone template for the entire Grand Army of the Republic. During the Clone Wars, in 22 BBY, the Galactic Republic deployed a [Jedi](/article/jedi]-led army to the [planet](/article/planet] Christophsis, tasking them with the mission to defend the world against the droid army of the Confederacy of Independent Systems. Integrated into the squad under the command of Clone Sergeant Slick, Chopper was among the troops dispatched by the Republic to the Christophsian homeworld. By this time, Chopper's disdain for battle droids had driven him to collect the digits of B1s from the battlefield as wartime souvenirs, which he then strung together to create a necklace. Chopper ensured his actions remained secret, given that his behavior contravened the regulations of the Republic Military.
Chopper's unit accompanied Jedi General Obi-Wan Kenobi and Clone Commander Cody during an attempted ambush of the Separatist Droid Army. Unexpectedly, the droids instead ambushed them, compelling the clones to fall back to their base on Christophsis. As they retreated from the engagement, one of Chopper's squadmates, the trooper "Gus", succeeded in detaching the head of a T-series tactical droid. Analysis of the droid's memory banks revealed that the Separatists had received advance warning about the Republic's battle plan, leading the clone officers to suspect the presence of a clone spying for the opposition. While the generals Kenobi and Anakin Skywalker conducted reconnaissance behind enemy lines, Commander Cody, assisted by Clone Captain Rex, initiated a search for the spy within the base.
Their investigation led them to the barracks housing Sergeant Slick's unit. Rex and Cody interrogated the clones individually, each providing an alibi to confirm their loyalty to the Republic. When they reached Chopper, the clone concealed his necklace of droid fingers and claimed he had immediately gone to the mess hall upon returning to base. However, his alibi was proven false when Sketch revealed that Chopper had not arrived in the mess hall until considerably later. Consequently, he was compelled to reveal his war trophy to the clone officers. Slick swiftly attempted to use this infraction to incriminate Chopper as the spy, only for Slick's own role as the traitor to be exposed.